linux-kernel - Re: [PATCH v4 1/4] drm: Introduce generic probe function for component based masters.

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Message-ID: <20151020100909.GW32532@n2100.arm.linux.org.uk>
Date:	Tue, 20 Oct 2015 11:09:09 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Emil Velikov <emil.l.velikov@...il.com>
Cc:	Liviu Dudau <Liviu.Dudau@....com>, David Airlie <airlied@...ux.ie>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Mark Yao <mark.yao@...k-chips.com>,
	Heiko Stuebner <heiko@...ech.de>,
	linux-rockchip <linux-rockchip@...ts.infradead.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/4] drm: Introduce generic probe function for
 component based masters.

On Tue, Oct 20, 2015 at 11:00:55AM +0100, Emil Velikov wrote:
> Hi Liviu,
> 
> On 20 October 2015 at 10:23, Liviu Dudau <Liviu.Dudau@....com> wrote:
> > A lot of component based DRM drivers use a variant of the same code
> > as the probe function. They bind the crtc ports in the first iteration
> > and then scan through the child nodes and bind the encoders attached
> > to the remote endpoints. Factor the common code into a separate
> > function called drm_of_component_probe() in order to increase code
> > reuse.
> >
> > Cc: David Airlie <airlied@...ux.ie>
> > Signed-off-by: Liviu Dudau <Liviu.Dudau@....com>
> > Acked-by: Russell King <rmk+kernel@....linux.org.uk>
> > ---
> >  drivers/gpu/drm/drm_of.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++
> >  include/drm/drm_of.h     | 13 +++++++
> >  2 files changed, 101 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
> > index be38840..493c05c 100644
> > --- a/drivers/gpu/drm/drm_of.c
> > +++ b/drivers/gpu/drm/drm_of.c
> > @@ -1,3 +1,4 @@
> > +#include <linux/component.h>
> >  #include <linux/export.h>
> >  #include <linux/list.h>
> >  #include <linux/of_graph.h>
> > @@ -61,3 +62,90 @@ uint32_t drm_of_find_possible_crtcs(struct drm_device *dev,
> >         return possible_crtcs;
> >  }
> >  EXPORT_SYMBOL(drm_of_find_possible_crtcs);
> > +
> > +/**
> > + * drm_of_component_probe - Generic probe function for a component based master
> > + * @dev: master device containing the OF node
> > + * @compare_of: compare function used for matching components
> > + * @master_ops: component master ops to be used
> > + *
> > + * Parse the platform device OF node and bind all the components associated
> > + * with the master. Interface ports are added before the encoders in order to
> > + * satisfy their .bind requirements
> > + * See Documentation/devicetree/bindings/graph.txt for the bindings.
> > + *
> > + * Returns zero if successful, or one of the standard error codes if it fails.
> > + */
> > +int drm_of_component_probe(struct device *dev,
> > +                          int (*compare_of)(struct device *, void *),
> > +                          const struct component_master_ops *m_ops)
> > +{
> > +       struct device_node *ep, *port, *remote;
> > +       struct component_match *match = NULL;
> > +       int i;
> > +
> > +       if (!dev->of_node)
> > +               return -EINVAL;
> > +
> > +       /*
> > +        * Bind the crtc's ports first, so that drm_of_find_possible_crtcs()
> > +        * called from encoder's .bind callbacks works as expected
> > +        */
> > +       for (i = 0; ; i++) {
> > +               port = of_parse_phandle(dev->of_node, "ports", i);
> > +               if (!port)
> > +                       break;
> > +
> > +               if (!of_device_is_available(port->parent)) {
> > +                       of_node_put(port);
> > +                       continue;
> > +               }
> > +
> > +               component_match_add(dev, &match, compare_of, port);
> > +               of_node_put(port);
> > +       }
> > +
> > +       if (i == 0) {
> > +               dev_err(dev, "missing 'ports' property\n");
> > +               return -ENODEV;
> > +       }
> > +
> > +       if (!match) {
> > +               dev_err(dev, "no available port\n");
> > +               return -ENODEV;
> > +       }
> > +
> > +       /*
> > +        * For bound crtcs, bind the encoders attached to their remote endpoint
> > +        */
> > +       for (i = 0; ; i++) {
> > +               port = of_parse_phandle(dev->of_node, "ports", i);
> > +               if (!port)
> > +                       break;
> > +
> > +               if (!of_device_is_available(port->parent)) {
> > +                       of_node_put(port);
> > +                       continue;
> > +               }
> > +
> Of the three drivers converted only the rockchip one has the above
> of_device_is_available() hunk. Based on the handling in previous loop
> I'm not entirely sure if it's needed, but if so shouldn't one mention
> the difference when converting the respective drivers ?

Yes, it should've been there, otherwise we'll end up binding encoders
which are connected to a CRTC which has been disabled - and that means
the DRM driver won't come up.

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